The present invention relates to a sheet handling device and, more particularly, to a device for inverting a sheet carried by a sheet transport conveyor.
Various types of copiers and duplicators are known in which the images from original documents may be copied onto sheets of copy paper. Such copiers and duplicators may use xerographic copying techniques or, alternatively, may reproduce the images from the original documents by ink jet printing or other printing techniques. Commonly, an original document may have an image on both sides of the document and it may be desired to produce copies of the document in which these images are reproduced on opposite sides of the sheets of copy paper. After a sheet of paper has been printed with an image on a first side of the sheet, as the sheet is transported on a conveyor past a printing station, it is necessary to invert the sheet of paper on the conveyor prior to transporting the sheet past the printing station for printing on the opposite side of the sheet. Alternatively, after the sheet is inverted, it may be transported past a second printing station for printing the second side of the sheet.
A number of devices have been developed which perform this sheet inversion process. One such device is shown in Reesen U.S. Pat. No. 4,214,831. The Reesen patent discloses a xerographic copier in which a sheet of copy paper is applied to a photosensitive belt and transported part a first transfer station to transfer an image from the belt onto the sheet. The sheet of paper is then diverted from the belt onto a guide member by means of vacuum rollers cooperating with and spaced along the guide member. After the sheet has been completely removed from the belt, the direction of rotation of the vacuum rollers is reversed and the sheet returned to the belt such that the edge of the sheet which was previously the trailing edge now becomes the leading edge. The belt then carries the sheet past a second image transfer station and a second image is transferred to the opposite side of the sheet. The sheet is thereafter removed from the belt, the images on both sides of the sheet are fixed simultaneously, and the sheet is transported to a copy paper output tray. While the Reesen device is useful in the limited environment of a xerographic belt copier, the inverter device is somewhat limited in possible applications in that successive sheets carried by the belt must be widely spaced apart in order to provide sufficient time for a sheet to be removed completely from the sheet guide and returned to the belt prior to the application of the next succeeding sheet to the inverter device.
A similar device is disclosed in Caldwell U.S. Pat. No. 3,917,257. The Caldwell patent discloses a sheet inverting arrangement having a vacuum transport which receives sheets stripped from a conveyor. After a sheet has been completely removed from the conveyor and is positioned on the vacuum transport, the direction of movement of the vacuum transport is reversed so that the sheet is reapplied to the conveyor with the trailing edge of the sheet becoming the leading edge. As with the Reesen device, the device disclosed in the Caldwell patent is limited in the speed at which it can invert sheets in that a sheet must be completely removed from the inverter prior to the application of the next successive sheet to the inverter. Additionally, the Caldwell inverter requires that a mechanically actuated deflector finger assembly be moved into contact with the sheet at its leading edge to deflect the sheet away from the conveyor. It will be appreciated that where such an inverter is utilized to deflect the leading edge of a sheet which is still somewhat wet from a first printing operation, damage to the leading edge of the sheet may occur.
Stange et al U.S. Pat. No. 4,054,285, and Acquavive U.S. Pat. No. 4,214,740 disclose generally similar sheet reversing devices in which a sheet is transported into a thin rectangular sheet receiving pocket by a roller arrangement. The document is then withdrawn from the pocket by the roller arrangement such that the leading edge of the sheet emerging from the pocket is the edge that was trailing during insertion. There is a suggestion that movement of a sheet within the rectangular pocket may be controlled pneumatically.
Additionally, the Acquaviva patent discloses a roller arrangement for withdrawing a sheet from the pocket which corrugates the sheet in a direction perpendicular to its movement such that the beam strength of the sheet is increased. The sheet therefore does not tend to be carried around the sheet driving rollers. The Acquaviva and Stange et al devices are limited in that a sheet must be completely removed from the rectangular pocket before the next successively presented sheet may be inserted into the pocket. Additionally, the leading edge of a sheet moving into the pocket strikes the end of the pocket and, as a consequence, the leading edge of a sheet may be damaged.
Clarkson et al U.S. Pat. No. 4,040,616 discloses a sheet inverting device in which a sheet traveling on a vacuum belt is transported downward around a roller until the leading edge of the sheet encounters a crescent-shaped reflector. The sheet of paper is peeled away from the belt and travels upward along the crescent-shaped deflector until it is completely removed from the belt. As a result of gravity, the sheet then slides back down the crescent-shaped deflector and is reapplied to the belt with the edge which was formerly leading becoming the trailing edge of the sheet. As with the previously discussed prior art inverter devices, the Clarkson et al inverter is limited in the speed at which it can handle the inversion of successively presented sheets.
As may be appreciated, it is desirable to provide a mechanism for inverting an original document for a copying device capable of duplex copying an original document having images on both sides. One such device is shown in Burton et al U.S. Pat. No. 4,052,128. In the Burton device, a belt transport is provided for positioning a document at a station where it is photographed. Thereafter, the transport conveys the document to a closed loop vacuum belt inverter. The document is pneumatically lifted from the transport and is carried around the belt inverter. The document is then reapplied to the transport which conveys the document back to the photographing station with its opposite side facing upward. The Burton et al device is rather cumbersome and also requires careful control of the transport and inverting belt system and appropriate timing of the application of partial vacuum and pressurized air to a number of vacuum plenums. Further, the transport must be driven repeatedly in both directions.
Accordingly, it is seen that there is a need for a simple sheet inverter device which is capable of handling the inversion of a succession of sheets at a high rate of speed, with the sheets being presented rapidly to the inverter device.